The water in the reflecting pool in front of the Abraham Lincoln Memorial in the scene where Ben and Riley are talking on the steps was digitally added later because the water was drained for maintenance at the time of filming. The pool was also digitally added on the movie Forrest Gump.
The movie suggests that something is written on the back of the Declaration of Independence. It is true that something is written on its back. The writing on the back of the Declaration of Independence reads: "Original Declaration of Independence dated 4th July 1776" and it appears on the bottom of the document, upside down. While no one knows for certain who wrote it, it is known that early in its life, the large parchment document (it measures 29 3/4 inches by 24 ½ inches) was rolled up for storage. So, it is likely that the notation was added simply as a label.
Ben, Patrick, and John Gates were all named after founding fathers (Benjamin Franklin, Patrick Henry, and John Adams). Abigail Chase is a combination of Abigail Adams, wife of John Adams, and Samuel Chase, a signer of the Declaration of Independence and later an Associate Justice of the United States Supreme Court.
When Gates is purchasing a replica Declaration of Independence in the gift shop, on the counter next to the register is a stack of books for sale. The book is 'The Secret Architecture of our Nation's Capital' by David Ovason and is about the Masons and the building of Washington DC. Ovason also wrote "Secret Symbols of the Dollar Bill", and US currency is used as one of the clues in the film.
Before the movie got its rating, it was under the Touchstone Pictures banner (which is part of Disney). When the film got its rating (which is PG), it was then put under the Walt Disney Pictures banner, as it is clear that it is a more family-friendly movie.
While Gates is attempting to decipher the first clue on board the Charlotte, after Shaw suggests "Prison," Riley says, "Albuquerque. See, I can do it too. Snorkel." This is a reference to the 1998 'Weird Al' Yankovic song, "Albuquerque," which talks about a man's journey to Albuquerque with his lucky snorkel.
In the D.C. segment during the planning stage of the burglary the movie cuts to an external shot of a building on the Potomac River - presumably where the bad guys are planning their attempt. This building is the Watergate Hotel.
The Liberty Bell shown in the movie was actually made of styrofoam. The movie was shot a few days before the Liberty Bell was put in. This is proven by the fact that protective shades were installed in the observation window when the bell was installed. In the movie Ian looks exactly where the shades are supposed to be if the real bell was there.
On the yellow piece of paper, on which Ian (Sean Bean) was writing out the secret message contained on the pipe found on the "Charlotte", there was drawn, at the top of the page, two crossed swords with a circle between them. This drawing is the logo for Bean's hometown Football Club, Sheffield United known also as The Blades.
The book that Ben shows Riley in the Library of Congress that has the information about the Preservation Room is called 'The Earth System'. It is some sort of a textbook and it is authored by Lee Kump, James F. Kasting, and Robert G. Crane. The ISBN is 0131420593.
At the end of the movie when Ben starts to tell Riley about the house he bought, the house actually belonged to Charles Carroll, the last surviving man who had signed the declaration. This also happens to be the man who told Ben's ancestor the secret about the charlotte in the beginning of the movie.
When Ben is investigating the dead end treasure room near the end and discovers the keyhole for the Charlotte pipe, a few bars of the underscore are actually from the film Pirates of the Caribbean. Both are Jerry Bruckheimer and Disney projects.
EASTER EGG: To see some hidden special features on the R2 DVD navigate to the logbook in the upper right corner of the main menu and press select to enter, then enter the code 405 and select the 'master code' for a list of all the special features available (some are otherwise only available in several hidden menus that must be found through mini-games on each menu).
When Riley (Justin Bartha) at the end of the movie says he got a measly 1/2 percent of the treasure money. If Benjamin Franklin Gates' (Nicholas Cage) earlier estimate back in the church with Sadusky (Harvey Keitel) of 10 billion dollars is accurate, Riley would have made 50 million dollars.
Easter egg: In the bonus (Treasure Hunt) portion on the DVD after watching all the bonus features you are asked to unscrambble the pairs of letters given after you watch each one. The unscrambbled word is TR.EA.SU.RE